Conventionally, an on-vehicle information displaying system is known (see Patent Document 1 for example). The system receives, by using a road-to-vehicle communication, service information (e.g., information about a service such as hazard prevention assistance in approaching a curve) sent from a roadside device and displays information about available services on an on-vehicle display device.
An navigation device having, for each area, background data (data for displaying a background of a road map) and route search data (data constituting of bifurcation information used for calculating recommended route) which are individually updated via a wireless communication is also known (see Patent Document 2 for example). The device compares the version of the background data it holds with the version of the route search data it holds. If the device determines that there is a mismatch between the versions (which are supposed to be the same), the device informs a user that there is a mismatch between the versions by toning down an indication (either a background image or a recommended route image) based on data with older version.
An on-vehicle device which receives service codes sent from a roadside device by using a road-to-vehicle communication is also known (see Patent Document 3 for example). The device determines a service as an available service if a service code stored in an IC card inserted into the on-vehicle device matches a service code received by the on-vehicle device, and stores in a storage part the service code and location information received together with the service code.
This on-vehicle device displays on a display device guidance related to the service so that the service can be utilized effectively when the on-vehicle device detects at a later date that the vehicle has approached a service providing location. This detection is based on the service code and the location information stored in the storage part.    [Patent Document 1] Japanese Patent Publication No. 2004-184176    [Patent Document 2] Japanese Patent Publication No. 2005-265574    [Patent Document 3] Japanese Patent Publication No. 2008-018609